too hostile for most metals: jet engines and the
National Aerospace Plane, or X-30.
If the remarkable X-30 ever flies-and that
is not a certainty-it will launch America into
the era of hypersonic travel (following pages).
Attaining orbital speed of 17,000 miles an
hour, it will subject materials to stresses of
unprecedented ferocity.
Jet engines, properly called gas turbines,
have demanded miracle materials since they
first flew in World War II. They are extraordi
nary machines. Pratt & Whitney's powerful
F-100 can propel an F-15 fighter straight up
at a thousand feet per second. Yet military and
commercial jets must perform flawlessly. "If
something goes wrong," engineers like to say,
"you can't go off and park on a cloud."
Jet engineers turned to titanium for light
ness, then to superalloys of nickel and cobalt to
handle fierce temperatures. Even so, turbine
blades in an engine's "hot section" must be
air-cooled or they will melt; this waste of heat
and oxygen slashes combustion efficiency.
An ambitious government program aims to
double engine performance by the year 2000.
Composites dominate prospective materials,
as they do for the X-30. In a handful of leading
laboratories I saw newborn composite materi
als that someday will reign in sky and space:
Q At United Technologies Corporation in
Connecticut, a glass matrix grips silicon car
bide fibers to form the composite Compglas.
Strong and heat resistant, it holds promise
both for engines and airframes.
[ Textron of Massachusetts encases continu
ous silicon carbide fibers of its own manufac
ture in a powerful matrix of titanium- part of
the family of materials known as metal-matrix
composites. A strong candidate for the X-30's
skin or skeleton.
O Martin Marietta Laboratories in Baltimore
is perfecting the X-D process, in which micro
particles of titanium diboride, formed chemi
cally in a titanium-aluminum alloy, create a
composite that withstands prolonged heat.
Another X-30 possibility.
MaterialsReshaping OurLives
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